EiR: Doping cubic boron nitride, an extreme material for power electronics and radiation detection

该项目的重点是用于极端应用的立方氮化硼。氮化硼是被称为III-氮化物的半导体家族的成员，该家族由氮和第三族元素如铝、镓和铟组成。这一系列材料实现了固态照明行业，并使微波通信发生了革命性的变化。立方氮化硼是一种超宽带隙材料，对可见光透明，只在深紫外光吸收。它可能会对电动汽车、智能电网和空间技术的电力电子产生革命性的影响。其特殊的硬度、高导热性和耐腐蚀性也使这种材料能够在恶劣的环境中取代钻石。对氮化硼的研究也将有助于对III-氮化物半导体的基础知识。该项目是霍华德和摩根州立大学的合作项目，这两所历史悠久的黑人学院(HBCU)。该项目使摩根和霍华德的学生能够参与具有商业意义的尖端技术。该项目明确地让研究生和本科生都参与到“动手”的研究活动中。该项目将资助摩根和霍华德的高级设计项目，在那里，学生们将把物理电子发现转化为真正的系统。该项目将鼓励少数族裔更多地参与HBCU的研究生研究项目。为了实现立方氮化硼(c-BN)的全部潜力，需要同时具有n型和p型导电使能双极器件以及互补金属氧化物半导体(CMOS)逻辑。研究表明，在超宽带隙材料中，可能存在浅n型(硅掺杂)和p型(铍掺杂)，使c-BN成为唯一的异常值。在这项工作中，我们研究了掺杂和补偿策略，以评估c-BN的前景。此外，我们还测量了这种材料的物理性质，如迁移率和击穿电场，作为缺陷形态的函数(根据需要更新历史数据)。这项工作涉及小型(1毫米)商用单晶c-BN样品，以及摩根州立大学生长的大面积薄膜。所有的测量将通过与第一原理密度泛函理论(DFT)的计算进行比较来解释，第一原理密度泛函理论(DFT)提供了真正基于原子物理的理解。这项工作的挑战之一将是生产多种多样的纯材料。为了在化学气相沉积(CVD)过程中实现这一点，需要刻蚀或溅射不太稳定的六方氮化硼(h-BN)多晶型，以便产生立方相。我们将测试3种方法：i)氢气刻蚀，ii)使用氟基前驱体，iii)离子束辅助，在单晶高温高压金刚石衬底上。表面准备和后退火将由DFT计算来指导。本征点缺陷(如空位)的补偿和掺杂很可能在这种UWBG材料中发挥重要作用，而密度泛函理论将是理解掺杂来源和电输运的关键工具。二极管和金属-半导体-金属结构将被用作测试设备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project focuses on cubic boron nitride for extreme applications. Boron nitride is member of the family of semiconductors known as III-nitrides, which consist of nitrogen and a Group III element such as aluminum, gallium, and indium. This family of materials has realized the solid-state lighting industry and revolutionized microwave communications. Cubic boron nitride is an ultra-wide bandgap material, transparent to visible light and absorbing only in the deep ultraviolet. It could have a transformative impact on power electronics for electric vehicles, smart grids, and space technologies. Its exceptional hardness, high thermal conductivity and corrosion resistance could also allow this material to replace diamond in harsh environments. Studies of boron nitride will also contribute to fundamental knowledge of III-nitride semiconductors. The project is a collaboration between Howard and Morgan State University, two Historically Black Colleges (HBCUs). The project enables Morgan and Howard students to participate in a cutting edge technology with commercial implications. The project explicitly engages both graduate students and undergraduates in "hands on" research activities. The project will fund senior design projects at Morgan and Howard, where students will translate physical electronics discoveries into real systems. The project will encourage greater minority participation in graduate research programs at HBCUs. To realize the full potential of cubic boron nitride (c-BN), it is desirable to have both n-type and p-type conduction enabling bipolar devices as well as Complementary Metal Oxide Semiconductor (CMOS) logic. It has been demonstrated that shallow n-type (silicon doping), and p-type (beryllium doping) are possible, making c-BN a unique outlier among ultrawide bandgap materials (UWBGs). In this work, we investigate doping and compensation strategies to evaluate the promise of c-BN. In addition we measure physical properties of this material such as mobility and breakdown field as a function of defect morphology (updating historical data as necessary). The work involves both small (1 mm) commercial single-crystal c-BN samples, as well as large area thin films grown at Morgan State. All measurements will be interpreted by comparing with first-principles density functional theory (DFT) calculations that provide a true atomic physics-based understanding. One of the challenges of the work will be to produce polytypic pure material. In order to accomplish this during chemical vapor deposition (CVD), the less stable hexagonal boron nitride (h-BN) polymorph is etched or sputtered away allowing the production of the cubic phase. We will test 3 methods to do this: i) etching by H2, ii) use of fluorine-based precursors and iii) ion-beam assistance, on single-crystal HPHT diamond substrates. Surface preparation and post-annealing will be guided by DFT calculations. Compensation and doping by intrinsic point defects (e.g. vacancies) are likely to play a strong role in this UWBG material, and DFT will be a critical tool to understanding the origin of the doping, and electrical transport. Diodes and metal-semiconductor-metal structures will be used as test devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.